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62 Physical harms resulting from colorectal cancer screening – a comparison between a new systematic review and former randomised controlled trials
  1. Anne Katrine Lykke Bie1,
  2. Frederik Martiny1,
  3. John Brodersen1,2
  1. 1Centre of Research and Education in General Practice, Copenhagen, Denmark
  2. 2Primary Health Care Research Unit, Zealand Region, Denmark


Screening for cancer has become a popular prevention strategy, aiming to reduce mortality and morbidity by earlier detection of asymptomatic cancers. The intended benefits of screening are: to reduce cancer-mortality and -morbidity and to provide less aggressive treatment. The unintended harms are: physical complications, psychosocial harm, false-positive and false-negative screening results, overdiagnosis, overtreatment, living longer as a cancer patient due to earlier detection with no altered prognosis and at worst increased morbidity and mortality.

6% of participants of the colorectal cancer (CRC) screening programmes, using faecal immunochemical tests, will receive a positive test result, but only approximately 5% (0.3% of screening participants) have cancer. The remainder will have received a false-positive result or have colon polyps that are either benign or potential precancer. The polyps are biopsied or removed during colonoscopy, but recent research suggests that a significant part of these polyps are overdiagnosed and overtreated.

Therefore, it is important to assess how harms have been reported to improve knowledge on potential unintended physical harm in CRC screening especially among the screening participants who are overdiagnosed.

Using a recent systematic review on the risk of physical harms due to CRC screening, this analysis aims to report the number of randomised controlled trials (RCTs) and the systematic reviews on the same subject and to compare the reporting of harms in these studies. Furthermore, the aim of this study is to assess whether these RCT’s and systematic reviews manage to identify all the potential types of physical harm, leading to trustworthy analysis of the of the studies.

Meta-analyses, systematic reviews and RCT’s are at the top of the scientific effect-study hierarchy. In effect, these studies often directly lead to major changes in public health, as has been the case for colorectal cancer screening, being implemented on a global scale. However, the recent systematic review questioned the ability of these studies to adequately estimate the risk of physical harm. As a result, it is important to assess the quality of these studies by comparing them to the recent systematic review to gain a better insight in the adequacy of the reporting of physical harms.

The recent systematic review (on physical harms in CRC screening) as carried out according to the PRISMA-harms extension and the Cochrane Handbook on Systematic Reviews. The study protocol was published on PROSPERO prior to data extraction.

For the present study we have searched for and included any randomised controlled trial fulfilling the above detailed criteria regardless if it has been included in the reference review or not. Also, we have searched for other systematic reviews that quantify the physical harms of colorectal cancer screening to compare how these harms are reported and the adequacy of measurement is assessed and reported in the review. The analysis does not aim to compare estimates of harm; rather it focuses on differences in reporting. Our analyses are focused on the comprehensiveness of reporting of harms and the adequacy of these.

Results and conclusions will be presented at the conference.

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